In the art, expensive equipment is used to provide detection instruments, which are also bulky since laboratory like conditions need to be provided in order to provide reliable results. Detectors which are used as field detectors and which are more economically sized exist but do require expensive calibration techniques which prevents straightforward mass production of these items. Therefore, these type of detectors are not as widely used as would be convenient, since most applications are cost prohibitive.
In the art, one detection sensor uses micro-hotplate technology, which is a semiconductor sensor on a micro-hotplate where chemical reactions occur of the traces to be detected. In particular such MOS type detector exploits the variation of electrical resistance of the sensor while, at a certain heating temperature, redox reaction take place on the surface of the sensor.
However, such hotplate technology is very sensitive to variations of the temperature and it is therefore important to provide detection of the traces at a prefixed temperature. In particular, the heater resistance is temperature dependent, which implies that current adjustments need to be provided to provide a stable temperature. This can be done by a balancing circuit which balances the heat resistor to a predefined resistor value.
U.S. Pat. No. 4,847,783 discloses a balancing circuit comprising an adjustable resistor for tuning the heater element to a predefined resistor value. The heater element operates a platinum resistance element having a predetermined resistance-temperature characteristic. However, in practice, although platinum resistance elements may show an almost perfect linear temperature behaviour, the real temperature may vary from sample to sample since the offsets of these elements may vary considerably. Thus, by presetting the heater element to a predetermined value, a repeatable yet unknown precise temperature is provided.
Hence, for different sensors, a certain chemical substance may be sensed at varying temperatures caused by the differing offsets of the heater elements, which may give rise to a differing detection results for the various sensors. Therefore, to provide a reliable sensor with replicable results, from which sensor results can be coupled to a standardized database comprising footprints of identified chemical compositions or substances, the temperature relation is very critical. However, an individual calibration setup wherein each sensor is tested in conditioned temperature and gas environments is very cumbersome.